KR20190025413A - Adhesive Sheet - Google Patents

Abstract

The present invention relates to an adhesive sheet which adheres one side of the adhesive sheet to an SUS substrate having a tangent delta value of 0.3 or more and less than 1 at 25°C and standing in the vertical direction such that an adhesive area is 10 mm x 10 mm, cures the same at the room temperature for 24 hours after autoclaving the same at 50°C and 5 atm for 20 minutes, and vertically hangs a weight of 4.9 N for 1 hour and has the ratio of a pushing area to an initial adhesive area of 0.1 to 5%. In addition, the adhesive sheet according to the present invention has excellent durability and improved bending resistance.

Description

{Adhesive Sheet}

The present invention relates to a pressure-sensitive adhesive sheet, and more particularly, to a pressure-sensitive adhesive sheet having excellent durability and improved bending resistance.

An optically clear adhesive (OCA) having high transparency is used for interlayer adhesion to laminate components in a display device. Such a transparent pressure sensitive adhesive sheet for optical properties is required to have high transmittance and low haze and to satisfy various properties such as adhesiveness to various substrates, heat resistance and damp heat resistance.

In recent years, a flexible display device capable of maintaining the display performance even if it is bent like paper by using a flexible material such as plastic instead of a conventional glass substrate without flexibility is rapidly emerging as a next generation display device, and applied to a flexible display device There has been a demand for development of a pressure-sensitive adhesive sheet having excellent durability and improved bending resistance so as to be suitable for the following.

Korean Patent Laid-Open Publication No. 2014-0044269 discloses a pressure-sensitive adhesive comprising a (meth) acrylate containing an alkyl group having 12 or more carbon atoms, a (meth) acrylate having an alkyl group having 1 to 8 carbon atoms and having a hydroxyl group, Sensitive adhesive sheet having a pressure-sensitive adhesive layer containing a crosslinked structure formed by cross-linking a composition. However, the pressure-sensitive adhesive sheet has a problem that it is difficult to secure excellent durability and flex resistance when applied to a flexible display device.

Therefore, there is a demand for development of a pressure-sensitive adhesive sheet having excellent durability and improved bending resistance.

Korea Patent Publication No. 2014-0044269

An object of the present invention is to provide a pressure-sensitive adhesive sheet having excellent durability and improved bending resistance.

On the other hand, the present invention is characterized in that one side of an adhesive sheet is adhered to a SUS base material having a tangent delta value at 25 ° C of 0.3 or more and less than 1 and standing in a vertical direction so as to have an adhesive area of 10 mm x 10 mm, After autoclaving for 20 minutes at 5 atm and curing for 24 hours at room temperature, the ratio (R) of the pressed area to the initial adhesion area after hanging the 4.9 N weight in the vertical direction for 1 hour, Is 0.1 to 5%.

In one embodiment of the present invention, the pressure-sensitive adhesive sheet is formed from a pressure-sensitive adhesive composition comprising an acrylic copolymer containing 20 to 40% by weight of a hydroxyl group-containing (meth) acrylate monomer, a monofunctional (meth) acrylate monomer and a photoinitiator .

In one embodiment of the present invention, the adhesive sheet can be used in a flexible display device.

The pressure-sensitive adhesive sheet according to the present invention was prepared by adhering one side of an adhesive sheet so that the tangent delta value at 25 ° C was adjusted to be 0.3 or more and less than 1, and the adhesive area was 10 mm x 10 mm on the SUS base material set up in the vertical direction, After autoclaving at 50 DEG C and 5 atm for 20 minutes, curing at room temperature for 24 hours, and then placing the weight of 4.9 N on the pressure-sensitive adhesive sheet in the vertical direction for 1 hour, (R) is adjusted to 0.1 to 5%, which is excellent in durability and has improved flex resistance.

Hereinafter, the present invention will be described in more detail.

In one embodiment of the present invention, the tangent delta value at 25 DEG C is 0.3 or more and less than 1,

One side of the pressure-sensitive adhesive sheet was adhered to the SUS base material set in the vertical direction so as to have an adhesive area of 10 mm x 10 mm, autoclaved at 50 DEG C and 5 atm for 20 minutes, cured at room temperature for 24 hours, Sensitive adhesive sheet in which the ratio of the pressed area to the initial adhesive area after hanging the weight of 4.9 N in the vertical direction for 1 hour is 0.1 to 5%.

The tangent delta value means a ratio of loss elastic modulus / storage elastic modulus of the pressure sensitive adhesive sheet, and is an index of ease of deformation (ease of stretching) of the pressure sensitive adhesive sheet. The method for measuring the tangent delta value of the adhesive sheet in the present invention is not particularly limited and can be measured by, for example, the method described in Experimental Examples described later.

In one embodiment of the present invention, the durability and flex resistance of the pressure-sensitive adhesive sheet can be improved by adjusting the tangent delta value of the pressure-sensitive adhesive sheet to 0.3 or more and less than 1 at room temperature of 25 占 폚. If the tangent delta value at 25 DEG C is less than 0.3, the bending resistance may be insufficient, and when the tentative delta value is more than 1, the durability may be deteriorated.

The pressure-sensitive adhesive sheet according to one embodiment of the present invention is obtained by adhering one side of an adhesive sheet so as to have an adhesive area of 10 mm x 10 mm to an SUS base material set up in a vertical direction, autoclaving the adhesive sheet at 50 DEG C and 5 atm for 20 minutes, , And then the ratio (R) of the pressed area to the initial adhesive area after standing for 1 hour by hanging the weight of 4.9 N in the vertical direction on the pressure-sensitive adhesive sheet is 0.1 to 5%.

The durability and flex resistance of the pressure-sensitive adhesive sheet can be improved by controlling the ratio (R) of the pressed area to the initial bonding area to 0.1 to 5%. If the ratio (R) of the area of the initial bonding area to the initial bonding area is less than 0.1%, the bending resistance may be insufficient. If the ratio R is more than 5%, the durability may be deteriorated.

In one embodiment of the present invention, the pressure-sensitive adhesive sheet comprises an acrylic copolymer (A), a monofunctional (meth) acrylate monomer (B) and a photoinitiator (B) containing 20 to 40% by weight of a hydroxyl group- C). ≪ / RTI >

The acrylic copolymer (A)

In one embodiment of the present invention, the acrylic copolymer (A) is a component which serves to control the viscosity-to-elasticity balance of the pressure-sensitive adhesive composition, and is an acrylic copolymer comprising 20 to 40% by weight of a hydroxyl group- Lt; / RTI > Here, (meth) acrylate means acrylate and methacrylate.

Examples of the hydroxyl group-containing (meth) acrylate monomer include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 4-hydroxybutyl Hydroxypropyleneglycol (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyleneglycol (meth) acrylate, 2- (Meth) acrylate, and the like. Of these, 2-hydroxyethyl (meth) acrylate and the like are preferable. These hydroxy group-containing (meth) acrylate monomers may be used alone or in combination of two or more.

The hydroxy group-containing (meth) acrylate monomer is preferably contained in an amount of 20 to 40% by weight based on 100% by weight of the total monomers used in the production of the acrylic copolymer. If the content of the hydroxy group-containing (meth) acrylate monomer is less than 20% by weight, the adhesion may be deteriorated. If the content is more than 40% by weight, the flexibility may be deteriorated.

The acrylic copolymer containing 20 to 40% by weight of the hydroxyl group-containing (meth) acrylate monomer may contain, in addition to the hydroxyl group-containing (meth) acrylate monomer, a (meth) acrylate monomer containing an alkyl group having 1 to 12 carbon atoms.

Examples of the (meth) acrylate monomer having an alkyl group having 1-12 carbon atoms include n-butyl (meth) acrylate, 2-butyl (meth) acrylate, t- (Meth) acrylate, ethyl (meth) acrylate, methyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (Meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate and lauryl (meth) acrylate. Of these, 2-ethylhexyl - octyl (meth) acrylate or mixtures thereof. These may be used alone or in combination of two or more.

The (meth) acrylate monomer having an alkyl group having 1 to 12 carbon atoms is preferably contained in an amount of 60 to 80% by weight based on 100% by weight of the total monomers used in the production of the acrylic copolymer. If the content of the (meth) acrylate monomer having an alkyl group having from 1 to 12 carbon atoms is less than 60% by weight, the bending resistance may be lowered. If the content is more than 80% by weight, durability may be deteriorated.

The acrylic copolymer may further contain other polymerizable monomers other than the monomers in an amount not lowering the adhesive force, for example, 10% by weight or less based on the total amount.

The method for producing the acrylic copolymer is not particularly limited, and can be produced by methods such as bulk polymerization, solution polymerization, emulsion polymerization or suspension polymerization, which are commonly used in the art, and solution polymerization is preferred. In addition, a solvent, a polymerization initiator, a chain transfer agent for molecular weight control and the like which are usually used in polymerization can be used.

The acrylic copolymer generally has a weight average molecular weight (polystyrene reduced, Mw) of 50,000 to 2,000,000, preferably 400,000 to 2,000,000 as measured by Gel Permeation Chromatography (GPC). When the weight-average molecular weight is less than 50,000, cohesion between co-polymers may be insufficient, which may cause problems in adhesion durability. If the weight average molecular weight is more than 2,000,000, a large amount of a diluting solvent may be required in order to ensure fairness in coating.

Single sensory  ( Meta ) Acrylate Monomer (B)

In one embodiment of the present invention, the monofunctional (meth) acrylate monomer (B) serves as a reactive diluent.

Examples of the monofunctional (meth) acrylate monomer include aliphatic monofunctional (meth) acrylate, alicyclic monofunctional (meth) acrylate, monofunctional (meth) acrylate having an ether group, monofunctional An aromatic monofunctional (meth) acrylate, and the like can be used.

Examples of the aliphatic monofunctional (meth) acrylate include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, butyl (Meth) acrylate, 2-ethylhexyl (meth) acrylate, n-butyl (meth) acrylate, (Meth) acrylate, dodecyl (meth) acrylate, n-octyl (meth) acrylate, nonyl (meth) acrylate, decyl (Meth) acrylate, isooctyl (meth) acrylate, lauryl (meth) acrylate, tridecyl (meth) acrylate, stearyl (Meth) acrylate, hexadecyl (meth) acrylate (Meth) acrylate, isoamyl (meth) acrylate, and the like.

Examples of the alicyclic monofunctional (meth) acrylate include isobonyl (meth) acrylate, cyclohexyl (meth) acrylate, and tetrahydrofurfuryl (meth) acrylate.

Examples of the monofunctional (meth) acrylate having an ether group include 3-methoxybutyl (meth) acrylate, 2-methoxyethyl (meth) acrylate, 3-methoxypropyl (meth) Butyl (meth) acrylate, methoxypolyethylene glycol acrylate having an addition molar number of oxyethylene of 1 to 15, ethoxy-diethylene glycol (meth) acrylate, ethylcarbitol (meth) acrylate, .

Examples of the monofunctional (meth) acrylate having a hydroxy group include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate and 4-hydroxybutyl have.

Examples of the aromatic monofunctional (meth) acrylate include benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, phenoxypolyethylene glycol acrylate, phenyl (meth) acrylate, 2-hydroxy- Propyl (meth) acrylate, and the like.

The monofunctional (meth) acrylate monomer (B) may be contained in an amount of 50 to 80 parts by weight based on 100 parts by weight of the entire acrylic copolymer (A). When the monofunctional (meth) acrylate monomer (B) is used within the above range, the durability and flex resistance are excellent.

Photoinitiator (C)

In one embodiment of the present invention, the photoinitiator (C) can be used without limitation as long as it is used in the technical field. Type 1 type photoinitiator, in which radicals are generated by decomposition of molecules due to difference in chemical structure or molecular binding energy, and type 2 photoinitiator, which is a hydrogen reclamation type, coexisting with tertiary amines. Specific examples of the Type 1 type photoinitiator include 4-phenoxydichloroacetophenone, 4-t-butyldichloroacetophenone, 4-t-butyl trichloroacetophenone, diethoxyacetophenone, 2-hydroxy- 2-methylpropan-1-one, 1- (4-dodecylphenyl) -2-hydroxy-2-methyl (2-hydroxy-2-propyl) ketone, 1-hydroxycyclohexyl phenyl ketone and the like, benzoin, benzoin methyl Benzoin ethers such as benzoin ethyl ether and benzyldimethyl ketal, acylphosphine oxides, and titanocene compounds. Specific examples of the Type 2 type photoinitiator include benzophenone, benzoyl benzoic acid, benzoyl benzoic acid methyl ether, 4-phenylbenzophenone, hydroxybenzophenone, 4-benzoyl- Benzophenones such as methyl-4-methoxybenzophenone, thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, and isopropylthioxanthone Oxanone, and the like. These may be used alone or in combination of two or more. The Type 1 type photoinitiator and the Type 2 type photoinitiator may be used alone or in combination.

The photoinitiator (C) may be contained in an amount of 0.01 to 3.0 parts by weight based on 100 parts by weight of the entire acrylic copolymer (A). When the photoinitiator (C) is contained in an amount less than 0.01 part by weight, it may be difficult to effectively initiate the crosslinking reaction. When the photoinitiator (C) is contained in an amount exceeding 3.0 parts by weight, discoloration or the like occurs due to the residual initiator, .

In one embodiment of the present invention, the pressure-sensitive adhesive composition may further contain, in addition to the above components, a silane coupling agent, a tackifier resin, an antioxidant, an antioxidant, and the like in order to control the adhesion, cohesion, viscosity, , A corrosion inhibitor, a leveling agent, a surface lubricant, a dye, a pigment, a defoaming agent, a filler, a light stabilizer, and the like.

The pressure-sensitive adhesive sheet according to one embodiment of the present invention is formed by using the above-described pressure-sensitive adhesive composition, whereby durability is excellent and bending resistance is improved.

The pressure-sensitive adhesive sheet according to an embodiment of the present invention may be one in which a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition is interposed between two base films.

Examples of the base film include a polyolefin film, a polyester film, an acrylic film, a styrene film, an amide film, a polyvinyl chloride film, a polyvinylidene chloride film and a polycarbonate film. Powder or the like.

The pressure-sensitive adhesive layer can be formed by coating the optical transparent pressure-sensitive adhesive composition on one base film. The coating method is not particularly limited as long as it is a method known in the art. For example, a bar coater, an air knife, a gravure, a reverse roll, a kiss roll, a spray, a blade, a die coater, a casting, . Specifically, a pressure-sensitive adhesive composition is coated on one base film and bonded to another base film, and then dried at 30 to 150 ° C for 1 second to 2 hours, preferably for 5 seconds to 1 hour, To 2000 mJ / cm < 2 >, preferably 200 to 1500 mJ / cm < 2 >

The thickness of the pressure-sensitive adhesive layer may be 5 to 200 占 퐉, preferably 30 to 100 占 퐉. If the thickness of the pressure-sensitive adhesive layer is less than 5 mu m, durability may be poor, and if it is more than 200 mu m, flex resistance may be poor.

The pressure-sensitive adhesive sheet according to an embodiment of the present invention may be subjected to surface treatment of the pressure-sensitive adhesive layer before bonding to improve adhesion.

The surface treatment method is not particularly limited, and the surface of the pressure-sensitive adhesive layer can be activated by a method such as corona discharge treatment, plasma treatment, ultraviolet irradiation, electron beam irradiation, or an anchoring agent application.

The pressure-sensitive adhesive sheet according to an embodiment of the present invention can be applied not only to a conventional flat panel display but also to a flexible display, and specifically to a display panel, a polarizer, a touch panel, a cover glass, a bezel, have. In particular, the adhesive sheet according to an embodiment of the present invention can be applied to a flexible display device.

Hereinafter, the present invention will be described more specifically with reference to Examples, Comparative Examples and Experimental Examples. It should be apparent to those skilled in the art that these examples, comparative examples and experimental examples are only for illustrating the present invention, and the scope of the present invention is not limited thereto.

Manufacturing example : Preparation of acrylic copolymer

Manufacturing example  1: Acrylic copolymer (A1)

(2-EHA) and 30 parts by weight of 2-hydroxyethylacrylate (2-HEA) were added to a 1 L reactor equipped with a cooling device for regulating the temperature of the reaction solution After the monomer mixture was added, nitrogen gas was purged for 1 hour to remove oxygen, and then maintained at 80 ° C. After the mixture was homogeneously mixed, 3.0 parts by weight of 1-hydroxycyclohexyl phenyl ketone was added as a reaction photo-initiator. Thereafter, the mixture was stirred and irradiated with a UV lamp (10 mW) to prepare an acrylic copolymer (A1).

Manufacturing example  2: Acrylic copolymer (A2)

A monomer mixture consisting of 70 parts by weight of n-octyl acrylate and 30 parts by weight of 2-hydroxyethyl acrylate (2-HEA) was added to a 1 L reactor equipped with a cooling device to regulate the temperature of the nitrogen gas , Nitrogen gas was purged for 1 hour to remove oxygen, and then maintained at 80 캜. After the mixture was homogeneously mixed, 3.0 parts by weight of 1-hydroxycyclohexyl phenyl ketone was added as a reaction photo-initiator. Thereafter, the mixture was stirred and irradiated with a UV lamp (10 mW) to prepare an acrylic copolymer (A2).

Manufacturing example  3: Acrylic copolymer (A3)

30 parts by weight of 2-ethylhexyl acrylate (2-EHA), 20 parts by weight of isobornyl acrylate (IBOA), 40 parts by weight of butyl acrylate And 10 parts by weight of 2-hydroxyethylacrylate (2-HEA) were charged, and then nitrogen gas was purged for 1 hour in order to remove oxygen, and then kept at 80 캜. After the mixture was homogeneously mixed, 3.0 parts by weight of 1-hydroxycyclohexyl phenyl ketone was added as a reaction photo-initiator. Thereafter, the mixture was stirred and irradiated with a UV lamp (10 mW) to prepare an acrylic copolymer (A3).

Example  1 to 3 and Comparative Example  1 to 2: Production of pressure-sensitive adhesive sheet

A pressure-sensitive adhesive composition was prepared by mixing the respective components in the composition shown in Table 1 below.

Example Comparative Example One 2 3 One 2 acryl
Copolymer Kinds A1 A1 A2 A3 A3 Content (parts by weight) 100 100 100 100 100 Photoinitiator Content (parts by weight) 2 2 2 2 2 The monofunctional (meth) acrylate monomer Kinds B1 B2 B1 B1 B2 Content (parts by weight) 50 50 50 50 50

Photoinitiator: 1-hydroxycyclohexyl phenyl ketone

B1: Dodecyl acrylate

B2: lauryl acrylate

After application of the thickness of the pressure-sensitive adhesive composition prepared above onto a silicone release agent-coated release film so that the 50㎛ and bonding the releasing film thereon is irradiated with light quantity of 500mJ / cm ² using a high pressure mercury UV lamp adhesive sheet .

Experimental Example  One:

The properties of the pressure-sensitive adhesive sheets prepared in Examples and Comparative Examples were measured by the following methods, and the results are shown in Table 2 below.

(One) retention (R)

The pressure-sensitive adhesive sheet was cut into a size of 50 mm x 100 mm, and the release film was peeled off. The pressure-sensitive adhesive sheet was then peeled off and bonded to the PET film (thickness 50 m) using a 2 kg rubber roller. Respectively. Thereafter, the heavy release film was peeled off and bonded to a SUS304 substrate to produce an adhesive area of 10 mm x 10 mm. Thereafter, the mixture was autoclaved at 50 DEG C and 5 atm for 20 minutes, cured at room temperature for 24 hours, attached with a weight of 4.9 N in the vertical direction, and allowed to stand for 1 hour. The ratio of the initial area to the pressed area of the pressure-sensitive adhesive layer is defined as R as shown in the following equation (1).

[Equation 1]

R (%) = (pressed area of pressure-sensitive adhesive layer / 100 mm ² ) x 100

(2) Tangent delta ( Tan delta )

The tangent delta is a value obtained by measuring G "(loss elastic modulus) / G '(storage elastic modulus) at 25 ° C. using a viscoelasticity measuring device (MCR-301, Anton Paar) A length of 30 mm and a width of 30 mm and a measurement sample bonded to a glass plate and adhered to a measuring tip in a temperature range of -30 to 100 캜 at a frequency of 1.0 Hz and a deformation rate of 2% , And reading the measured value at 25 캜.

(3) Coating property

The state of the coating layer was visually observed in the course of coating the pressure-sensitive adhesive composition, and the coating property was evaluated according to the following evaluation criteria.

<Evaluation Criteria>

○: No visible bubbles or streaks on the coating layer

?: The bubble and / or stripe pattern of the coating layer was visually confirmed by the naked eye

X: The bubble and / or stripe pattern of the coating layer was visually confirmed.

(4) Durability (heat resistance, Wet heat )

The heat resistance characteristics were observed at 100 ° C. for 500 hours and then observed for occurrence of bubbles or peeling. The anti-wet heat characteristics were measured at 85 ° C. and 85% RH for 500 hours. Were observed and evaluated by the following evaluation criteria.

<Evaluation Criteria>

Ⓞ: No bubbles or peeling.

○: Bubbles or peeling <5

?: 5 pieces? Bubbles or peeling <10 pieces

X: 10 pieces &lt; bubble &

(5) Flexibility at room temperature

The releasing film on one surface of the pressure sensitive adhesive sheet was peeled off, adhered to the hard coating film, folded in half so that the distance between the surfaces of the hard coating film was 6 mm, and visually confirmed whether a crack occurred in the folded portion when it was spread again .

<Evaluation Criteria>

Good: cracking of folded parts

Bad: Cracked or streaked folded area

(6) Mandrell

In order to evaluate the bending property and the cracking property, the releasing film on one side of the pressure-sensitive adhesive sheet was peeled off and adhered to the hard coating film. Then, the sample cut into a size of 1 cm x 10 cm was cut into iron bars (2? And the hard coating film was placed on the lower side and folded by hand to indicate the smallest diameter that does not cause cracks or streaks on the surface.

division Holding force (R,%) Tangent delta (25 ° C) Coating property durability Flexibility at room temperature Mandrell Heat resistance Wet heat Example 1 1.5 0.6 ○ Ⓞ Ⓞ Good 3φ Example 2 3.5 0.5 ○ Ⓞ Ⓞ Good 5φ Example 3 3 0.5 ○ Ⓞ Ⓞ Good 4φ Comparative Example 1 8 0.2 × × × Bad 12φ Comparative Example 2 9 0.15 × × × Bad 14φ

As can be seen from Table 2, it was confirmed that the pressure-sensitive adhesive sheets of Examples 1 to 3 according to the present invention had excellent coating properties and durability and excellent flexural resistance. On the other hand, it was confirmed that the pressure-sensitive adhesive sheets of Comparative Examples 1 and 2 had poor coatability, durability and flex resistance.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Do. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Accordingly, the actual scope of the invention is defined by the appended claims and their equivalents.

Claims (5)

A tan delta value at 25 DEG C of from 0.3 to less than 1,
One side of the pressure-sensitive adhesive sheet was adhered to the SUS base material set in the vertical direction so as to have an adhesive area of 10 mm x 10 mm, autoclaved at 50 DEG C and 5 atm for 20 minutes, cured at room temperature for 24 hours, Wherein the ratio of the pressed area to the initial adhesive area after hanging the weight of 4.9 N in the vertical direction for 1 hour is 0.1 to 5%. The pressure-sensitive adhesive sheet according to claim 1, wherein the pressure-sensitive adhesive sheet is formed from a pressure-sensitive adhesive composition comprising an acrylic copolymer containing 20 to 40% by weight of a hydroxyl group-containing (meth) acrylate monomer, a monofunctional (meth) acrylate monomer and a photoinitiator. The pressure-sensitive adhesive sheet according to claim 2, wherein the monofunctional (meth) acrylate monomer is contained in an amount of 50 to 80 parts by weight based on 100 parts by weight of the entire acrylic copolymer. The adhesive sheet according to claim 2, wherein the photoinitiator is contained in an amount of 0.01 to 3.0 parts by weight based on 100 parts by weight of the entire acrylic copolymer. The adhesive sheet according to claim 1, which is used for a flexible display device.